Formation of the embryo sac:-

• The nucleus of the functional megaspore divides mitotically to form two nuclei, which move to the opposite poles, forming the 2-nucleate embryo sac.
• Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac.
• These divisions are strictly free nuclear, i.e., nuclear divisions are not followed immediately by cell wall formation.
• After the 8-nucleate stage, cell walls are laid down, leading to the organization of the typical female gametophyte or embryo sac.
• 6 of the 8 nuclei are surrounded by cell walls and organized into cells.
• Remaining 2 nuclei (polar nuclei) are situated below the egg apparatus in the large central cell.